py3k server support

Eventually, we will have to convert the server code to py3k... Which is going to be a pain, probably even worse than #90.

We should probably move away from GTK at that point too, and replace all the pygobject plumbing with something a bit simpler and faster.

This ticket is here to record all the things that will need to be done to make this happen.

Apart from the usual string vs unicode nonsense, we will have to deal with the borken change they made to dict items vs iteritems in version 3: we rely on the fact that items() makes a copy, which is no longer true, we can probably switch to viewkeys() for most cases - except that this is python 2.7 only... so we'll need to drop support for 2.6 before that (ie: all centos 6).